I. Field
The present invention relates generally to circuits, and more specifically to a general-purpose wideband amplifier.
II. Background
Amplifiers are commonly used to amplify signals to obtain the desired signal level. Amplifiers are also widely used for various applications such as communication, computing, networking, consumer electronics, and so on. As an example, for wireless communication, amplifiers may be used on a transmit path to amplify a signal prior to transmission via a wireless channel and on a receive path to amplify a signal received via the wireless channel.
An amplifier may be designed to provide a fixed gain or a variable gain. Variable gain amplifiers (VGAs) are commonly used in communication circuits (e.g., receivers and transmitters) to provide variable gains, and thus adjustable signal levels, depending on operating conditions, system requirements, and/or other factors. For example, VGAs are commonly used for power control in wireless communication systems. In a Code Division Multiple Access (CDMA) system, the signal from each wireless device (e.g., cellular phone or mobile handset) is spectrally spread over the entire system bandwidth. The signal transmitted by each wireless device acts as interference to the signals transmitted by other wireless devices in the system. The transmit power of each wireless device is thus adjusted such that the received signal quality for the wireless device, as measured at a receiving base station, is maintained at a target level. This power control achieves the desired performance for the wireless device, minimizes interference to other wireless devices, and increases system capacity.
A wireless device may be located anywhere relative to a receiving base station and may need different amounts of transmit power at different locations to achieve the target received signal quality at the base station. More transmit power is typically required when the wireless device is located far away from the base station, and less transmit power is typically required when the wireless device is close to the base station. For a CDMA system, the wireless device may be required to adjust its transmit power over a wide range (e.g., by 90 decibels (dB) or more) in order to combat the so-called “near-far” effect. Such a wide power control range is typically achieved by distributing variable gains across an entire transmit chain, possibly from analog baseband to radio frequency (RF) front end. The power control may thus be performed by VGAs located throughout the transmit chain.
Amplifiers with simple architecture and good performance are challenging to design, but are highly desirable for cost, power, and other considerations. VGAs with these same characteristics are even more difficult to design. There is therefore a need in the art for an amplifier with simple architecture and good performance.